1. Field of the Invention
The present invention relates to a controller of a continuously variable transmission mounted on a vehicle provided with an accelerator manipulating element, which is manipulated by hand, and a vehicle provided with the same.
2. Description of Related Art
Conventionally, a V-belt type continuously variable transmission is used as a manipulating element for accelerating or decelerating a vehicle, such as a scooter type motorcycle, etc., that is provided with an accelerator manipulating element manipulated by hand (for example, an accelerator grip, an accelerator lever, etc.). One type of continuously variable transmission that is conventionally and frequently used is a so-called mechanical type continuously variable transmission, which comprises a centrifugal governor, wherein a speed change ratio is automatically regulated by a centrifugal force generated on the centrifugal governor at the time of rotation.
An engine rotational frequency of a conventional motorcycle or the like, on which a mechanical type continuously variable transmission is mounted, is fundamentally controlled by a throttle opening degree and a vehicle speed. While a speed change ratio can be steplessly regulated by a continuously variable transmission, a speed change ratio is controlled so that V-N characteristics prescribed by a vehicle speed (V) and an engine rotational frequency (N) fall in a predetermined region of speed change. For example, as shown in FIG. 7, a region (hatched region) S of speed change is defined by a V-N characteristic curve A1, wherein an accelerator is fully opened to accelerate under the condition of a normal load (i.e., in the case where one person takes a vehicle on a flat road), and by a V-N characteristic curve A2, wherein the accelerator is fully closed to decelerate under such condition. A speed change ratio is set so that V-N characteristics (in FIG. 7, a point prescribed by a vehicle speed, which is a parameter on the abscissa, and an engine rotational frequency, which is a parameter on the ordinate) do not deviate from the defined region S of speed change. That is, conventionally, deviation from the region S of speed change does not occur even at the time of acceleration from a stopping state and at the time of acceleration during traveling.
However, a motorcycle or the like, on which a mechanical type continuously variable transmission is mounted, experience slow acceleration when accelerating on a steep, upward slope and when accelerating with a double ride. Also, engine braking is less effective when an accelerator is returned. In view of these problems, an electronic controlled type continuously variable transmission has been developed, in which a belt wound diameter of a sheave is controlled by an electric motor or the like to freely regulate a speed change ratio irrespective of a running state.
In one such electronic controlled type continuously variable transmission, a plurality of operation modes are prepared in advance and a driver switches modes to modify the V-N characteristics stepwise. There may be two kinds of operation modes, for example, such as a normal mode and a power mode, which attaches greater importance to quality of acceleration than that with the normal mode. When a driver switches from the normal mode to the power mode, a speed change ratio is modified to be rather large (Low side) and an engine rotational frequency is controlled to be rather high in a range of the region of speed change.
However, with only two operation modes it is difficult to constantly generate a feeling of acceleration which satisfies the driver. To satisfy the driver, it is conceivable to prepare a multiplicity of operation modes that can be selected according to a situation.
Japanese Patent Publication No. 04-131558 discloses a continuously variable transmission provided with a manual type reduction lever, in which a speed change ratio is optionally adjustable in a predetermined region of speed change. With such a continuously variable transmission, the reduction lever can be set to an optional position between a fully closed position and a fully opened position. Therefore, it is possible to minutely regulate a speed change ratio unlike the related art, in which a speed change ratio can be regulated only stepwise. For example, the driver may manipulate the reduction lever at a time of rapid acceleration to obtain a high engine rotational frequency value. This type of continuously variable transmission includes, so to speak, an infinite number of operation modes between which the driver can optionally switch.
However, conventional continuously variable transmissions can control a speed change ratio only within the limit of the region of speed change described above. Therefore, in conventional motorcycles, a whole region in which speed change can be effectively attained is not made use of, and engine performance is therefore not maximized.
Also, with the conventional continuously variable transmissions, in order to get enough acceleration when traveling on a steep, upward slope, or the like, a driver must manipulate a mode selection switch, a reduction lever, or the like, which is troublesome.
Also, after the operation mode is switched to obtain a necessary acceleration, the driver may forget to return the mode selection switch to its original state. Therefore, for example, operation in a state where engine rotational frequency is higher than normal may continue over an unintendedly long period of time.